Dermoscopic, histological and immunohistochemical evaluation of cancerous features in acquired melanocytic nevi that have been repeatedly exposed to UVA or UVB.

Previous studies have reported that repeated solar and artificial UVB (280-320 nm) and UVA (320-400 nm) exposures can modify acquired melanocytic nevi (AMN). We therefore investigated the clinical, dermoscopic, histological and immunohistochemical changes in AMN exposed to UVB and UVA radiation. Twenty healthy volunteers with at least three AMN on the trunk were enrolled in the present study and randomized into two groups to receive equally effective doses of narrow-band (NB)-UVB or UVA1. Three exposures per week were delivered for a total of 4 weeks. During exposures, one AMN was left unprotected, a second one was shielded with an opaque adhesive tape and the third nevus was covered with a commercial sunscreen. After the irradiation cycle, the AMN were surgically removed and underwent histological and immunohistochemical assessment of melanocyte/melanogenesis-related proteins (MART-1, tyrosinase, HMB-45), cell cycle activation markers (Ki-67, topoisomerase IIalpha, p53, Cdk2) and transcription factors (microphthalmia-associated transcription factor, STAT3). Nevi that were exposed to NB-UVB or UVA1 also showed statistically significant increase in size and changes in their dermoscopic features, including overall darkening, increased pigment network expression, formation of branched streaks, and increased number and size of brown globules and dots. AMN that had been covered with opaque tape or sunscreen did not show changes in size or dermoscopic features following UVA1 or NB-UVB exposure. Histological and immunohistochemical analysis did not show any significant change in exposed AMN in comparison with AMN shielded with an opaque adhesive tape or covered with the sunscreen.